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Abstract
Noise exposure can affect the functioning of inner hair cells (IHC) within the cochlea, leading to a ‘noisy’ representation of the properties of sounds even when absolute thresholds are normal. This may lead to a reduced ability to discriminate sounds based on their statistical properties, especially for narrowband sounds presented at low levels, since such sounds excite only a small proportion of the IHCs. This idea was tested by requiring subjects to discriminate a Gaussian noise from a ‘low-noise noise’ with minimal envelope fluctuations. The noises were centred at 2, 3, or 4kHz. The stimulus duration required for threshold was measured as a function of sensation level (SL) for two groups of normal-hearing subjects, one rarely exposed to high-noise events (control group, C) and one frequently exposed to high-noise events (experimental group, X). For group X, threshold consistently rose for SLs below about 20dB, while for group C the threshold did not consistently rise at low SLs (although it did for a minority of subjects). The worsening in performance with decreasing level was significantly greater for group X than for group C.
| Abbreviations | ||
| 3AFC | = | Three-alternative forced-choice |
| BM | = | Basilar membrane |
| CF | = | Characteristic frequency |
| E | = | Envelope |
| ERB | = | Equivalent rectangular bandwidth |
| GSN | = | Gaussian noise |
| IHC | = | Inner hair cells |
| LI | = | Level impairment |
| LNN | = | Low-noise noise |
| OHC | = | Outer hair cells |
| PTS | = | Permanent threshold shift |
| SL | = | Sensation level |
| TFS | = | Temporal fine structure |
| TTS | = | Temporary threshold shift |
| Abbreviations | ||
| 3AFC | = | Three-alternative forced-choice |
| BM | = | Basilar membrane |
| CF | = | Characteristic frequency |
| E | = | Envelope |
| ERB | = | Equivalent rectangular bandwidth |
| GSN | = | Gaussian noise |
| IHC | = | Inner hair cells |
| LI | = | Level impairment |
| LNN | = | Low-noise noise |
| OHC | = | Outer hair cells |
| PTS | = | Permanent threshold shift |
| SL | = | Sensation level |
| TFS | = | Temporal fine structure |
| TTS | = | Temporary threshold shift |
Sumario
La exposición a ruido puede afectar el funcionamiento de las células ciliadas internas (IHC) en la cóclea, conduciendo a una representación “ruidosa” de las propiedades de los sonidos incluso cuando los umbrales auditivos son normales. Esto puede llevar a la reducción de las habilidades para discriminar sonidos con base en sus propiedades estadísticas, especialmente con sonidos de banda estrecha que se presentan en niveles bajos, en tanto esos sonidos excitan solo una pequeña proporción de IHC. Esta idea fue examinada solicitando a los sujetos la discriminación de un ruido Gaussiano de un “ruido de ruido bajo”, con mínimas fluctuaciones de su envoltura. Los ruidos estuvieron centrados en 2, 3 y 4 kHz. La duración del estímulo requerida para el umbral fue medida como una función de nivel de sensación (SL) en los dos grupos de sujetos normo-oyentes, uno rara vez expuesto a eventos de ruido elevado (grupo control, C) y uno frecuentemente expuesto a eventos de ruido elevado de banda amplia. (grupo experimental, X). En el grupo X, el umbral se elevó consistentemente para los SL por debajo de 20 dB, mientras que en el grupo C el umbral no se elevó consistentemente en niveles de SL bajos (aunque si lo hizo en una minoría de los sujetos). El empeoramiento del rendimiento con niveles decrecientes fue significativamente mayor para el grupo X que para el grupo C.